Part 14

{166} “A glass tube is to be bent into a syphon, and placed with the curve downwards, and in the bend is to be placed a small portion of mercury, not sufficient to close the connexion between the two legs; a solution of nitrate of silver is then to be introduced until it rises in both limbs of the tube. The precipitation of the mercury, in the form of an Arbor Dianæ, will then take place, slowly, only when the syphon is placed in a plane perpendicular to the magnetic meridian; but if it be placed in a plane coinciding with the magnetic meridian, the action is rapid, and the crystallization particularly beautiful, taking place principally in that branch of the syphon towards the north. If the syphon be placed in a plane perpendicular to the magnetic meridian, and a strong magnet brought near it, the precipitation will commence in a short time, and be most copious in the branch of the syphon nearest to the south pole of the magnet.”

{169a} Fatty matter has also been formed in the laboratory. The process consisted in passing a mixture of carbonic acid, pure hydrogen, and carburetted hydrogen, in the proportion of one measure of the first, twenty of the second, and ten of the third, through a red-hot tube.

{169b} Supplement to the Atomic Theory.

{170} Carpenter on Life; Todd’s Cyclopædia of Physiology.

{171} Carpenter’s Report on the results obtained by the Microscope in the Study of Anatomy and Physiology, 1843.

{172} See Dr. Martin Barry on Fissiparous Generation; Jameson’s Journal, Oct. 1843. Appearances precisely similar have been detected in the germs of the crustacea.

{175} Mr. Leonard Horner and Sir David Brewster, on a substance resembling shell.—Philosophical Transactions, 1836.

{179a} Dr. Allen Thomson, in the article Generation, in Todd’s Cyclopædia of Anatomy and Physiology.

{179b} The term aboriginal is here suggested, as more correct than spontaneous, the one hitherto generally used.

{182} Article “Zoophytes,” Encyclopædia Britannica, 7th edition.

{187} See a pamphlet circulated by Mr. Weekes, in 1842.

{195} Daubenton established the rule, that all the viviparous quadrupeds have seven vertebræ in the neck.

{201} Lord’s Popular Physiology. It is to Tiedemann that we chiefly owe these curious observations; but ground was first broken in this branch of physiological science by Dr. John Hunter.

{204} When I formed this idea, I was not aware of one which seems faintly to foreshadow it—namely, Socrates’s doctrine, afterwards dilated on by Plato, that “previous to the existence of the world, and beyond its present limits, there existed certain archetypes, the embodiment (if we may use such a word) of general ideas; and that these archetypes were models, in imitation of which all particular beings were created.”

{208} The numbers 1, 3, 6, 10, 15, 21, 28, &c. are formed by adding the successive terms of the series of natural numbers thus:

1 = 1 1+2 = 3 1+2+3 = 6 l+2+3+4 = 10, &c.

They are called triangular numbers, because a number of points corresponding to any term can always be placed in the form of a triangle; for instance—

. . . . .. .. .. ... ... .... 1 3 6 10

{215} Kirby and Spence.

{221} See an article by Dr. Weissenborn, in the New Series of “Magazine of Natural History,” vol. i. p. 574.

{224} “It is a fact of the highest interest and moment that as the brain of every tribe of animals appears to pass, during its development, in succession through the types of all those below it, so the brain of man passes through the types of those of every tribe in the creation. It represents, accordingly, before the second month of utero-gestation, that of an avertebrated animal; at the second month, that of an osseous fish; at the third, that of a turtle; at the fourth, that of a bird; at the fifth, that of one of the rodentia; at the sixth, that of one of the ruminantia; at the seventh, that of one of the digitigrada; at the eighth, that of one of the quadrumana; till at length, at the ninth, it compasses the brain of Man! It is hardly necessary to say, that all this is only an approximation to the truth; since neither is the brain of all osseous fishes, of all turtles, of all birds, nor of all the species of any one of the above order of mammals, by any means precisely the same, nor does the brain of the human fœtus at any time precisely resemble, perhaps, that of any individual whatever among the lower animals. Nevertheless, it may be said to represent, at each of the above-mentioned periods, the aggregate, as it were, of the brains of each of the tribes stated; consisting as it does, about the second month, chiefly of the mesial parts of the cerebellum, the corpora quadrigemina, thalami optici, rudiments of the hemispheres of the cerebrum and corpora striata; and receiving in succession, at the third, the rudiments of the lobes of the cerebrum; at the fourth, those of the fornix, corpus callosum, and septum lucidum; at the fifth, the tubor annulare, and so forth; the posterior lobes of the cerebrum increasing from before to behind, so as to cover the thalami optici about the fourth month, the corpora quadrigemina about the sixth, and the cerebellum about the seventh. This, then, is another example of an increase in the complexity of an organ succeeding its centralization; as if Nature, having first piled up her materials in one spot, delighted afterwards to employ her abundance, not so much in enlarging old parts as in forming new ones upon the old foundations, and thus adding to the complexity of a fabric, the rudimental structure of which is in all animals equally simple.”—Fletcher’s Rudiments of Physiology.

Table shows: scale of animal kingdom (the numbers indicate orders); order of animals in; ascending series of rocks; fœtal human brain resembles, in

(The numbers indicate orders)

Rocks: 1. Gneiss and Mica Slate system

Fœtal: 1st month, that of an avertebrated animal;

Scale: RADIATA (1, 2, 3, 4, 5)

Order: Zoophyta, Polypiaria

Rocks: 2. Clay Slate and Grawacke system